A developing cartridge known in the art is provided with a detection gear including a protrusion. There is also known an image forming apparatus provided with an actuator.
Specifically, when the developing cartridge receives a drive force from the image forming apparatus after the developing cartridge is attached to the image forming apparatus, the detection gear in the developing cartridge rotates. The rotation of the detection gear shifts the protrusion between a contact state in which the protrusion is in contact with the actuator, and a non-contact state in which the protrusion is not in contact with the actuator. These shifts between the contact state and the non-contact state of the protrusion, or the number of protrusions, indicate specifications of the developing cartridge.